Q From Bill McCord: As a native of that city I am often asked for the origin of the phrase to be sent to Coventry.
A It is very probable that the West Midlands city is the source of this expression for someone who has been ostracised. I say that with some care because there are at least two theories about where it came from. All of them do point to your native city, but none of them can be substantiated. The idiom is first recorded in 1765, but it is generally taken to refer to events during the English Civil Wars of the 1640s between forces loyal to the King and those loyal to Parliament.
The first appearance of the phrase is in 1647, in The History of the Rebellion and Civil Wars in England by Edward Hyde, First Earl of Clarendon, though the author is using the phrase in a literal, not a figurative sense. He says that Royalist troops who were captured in Birmingham (then a small town, not the great city that grew up later on the back of the Industrial Revolution) were taken for security to Coventry, a Parliamentarian stronghold. Understandably, they were not welcome. Another story, undated but usually taken to refer to events of a similar period, is that Coventry was strongly opposed to having troops billeted on townspeople, and that soldiers sent there were ostracised by the local population.
Take your pick. My own feeling is that neither is convincing, not least because of the century-long gap between Civil War events and the first appearance of the idiom — not impossible, though.